Higss lstom 4. 
Figs. 
Figs. 
Figs. 11 to 17. 
Figs. 18 and 19. 
18. 
19. 
Figs. 20 to 23. 
20 and 21. 
22 and 23. 
Figs. 24 to 28. 
24 and 25. 
26. 
27. 
28. 
Figs. 29 to 31. 
29 and 30. 
Bile 
BVO. Te 
8 to 10. 
8. 
9. 
10. 
PLATE XXX. 
PAGE. 
IN GUGASMAN CAT ENEN SIS cA Sr sciascinsaic cist see srencceaeeed eacenee ono 
Interior of the ventral valve from a gutta percha impression. g, umbonal scar; 
k, middle; 1, lateral scars; s, septum. 
Interior of the dorsal valve from a gutta percha impression. cr, crescent; h, 
central scars; j, anterior scars; ¢, transverse scars; other letters as in fig. 1. 
Profile of the type specimen from which the impressions of figs. 1 and 2 were 
made. The space between the dotted line and the natural cast shows the 
relative thickness of the shell. 
A portion of the exterior surface, x 5, to show the arrangement of the linear 
series of papillz on the concentric lines of growth. Near the top of the Galena 
limestone, near Hamilton, Minn. Minnesota Geological Survey collection. 
SCHIZAMBON! (2) DODGIL) De SDccenrce te an eee eet ee menses ome ae eins 
View of the ventral valve, showing the strongly lamellose concentric lines, spine 
bases and pedicle opening, x 2. 
A dorsal valve preserving some of the surface spines, x 2. 
Profile outline to show the relative convexity of valves and the projecting 
beak of the ventral valve, x 2. Upper Trenton at Sandy Hill, New York. Col- 
lection of C. Schuchert. 
SOHIZAMBON( (?) HOGRIUM GI Spot anita aaetota ee rte coisas eRe es 
The ventral valve, showing the submarginal beak and the pedicle opening. 
The dorsal valve of the same specimen in which the beak is marginal. 
Profile outline of the same specimen. p, pedicle valve. Middle beds of the Hudson 
River group, Cincinnati, Ohio. Collection of C. Schuchert. 
CETLAMBONTTES! DIVER SASS HAler SDEsec are ae iactemnice cece coe ene eee ne enics 
A dorsal view, showing the elevated area of the ventral valve, in which the del- 
tidium has been worn away, exposing the spondylium. (After Hall.) 
Ventral view of the same specimen. The distorted beak is not accidental, but a 
feature often developed in the species. (After Hall.) 
Interior of the ventral valve, showing the spondylium (sp) supported by a short 
septum (s). (After Hall.) 
Interior of the dorsal valve. cp, cardinal process; ad, adductor scars; 0, genital 
markings. Galena shales, near Cannon Falls, Minn. Collection of C. Schuchert. 
Interior of another dorsal valve in which the deltidium is preserved. The impres- 
sions of the vascular system are also shown on each side of the septum, and 
posterior to these are the genital markings. - 
A portion of fig. 15 in which the deltidium is broken away to show the muscular 
sears of the spondylium, x 2. 
An oblique view of the same specimen, to show the adjustor scars on the lateral 
limits of the spondylium, x 2. Galena shales, near Cannon Falls, Minn. Col- 
lection of W. H. Scofield. 
CLITAMBONITES DIVERSA, var. ALTISSIMA, 0. vat. 
Profile view, to show the great elevation of the ventral valve. 
Cardinal view of the same specimen. D, deltidium; ¥, foramen or pedicle open- 
ing. (After Hall.) Galena shales, south of Cannon Falls, Minn. Collection 
of C. Schuchert. 
SCENIDIUM PANTHONENSISL SATO ESOM Gy. .-.cate aocicticia te «nie c «ih slots deieenecaaee cle oloeace soece 
Ventral and cardinal views of a specimen, x 4. Trenton shales, near Cannon 
Falls, Minn. Collection of W. H. Scofield. 
Views of the exterior and interior of a dorsal valve. 
stone, Lebanon Tennessee. 
(After Hall.) Glade lime- 
ANASTROPHIA (?) SCOFIELDI, 0. Sp.........- Risiaticisteisia eieled eVeeneeree 
Views of the dorsal and ventral valves respectively. 
Profile view of the same specimen. 
Cardinal view of a distorted specimen, showing an area on the dorsal yalye, x 3. 
Profile outline, through the center of the shell, to show the extent of the spon- 
dylium, and the septum in the ventral valve, and the septal plates of the dorsal 
valve. Galena shales, near Cannon Falls, Minn, Minnesota Geological Survey 
collection. 
ANASTROBHEAS(>) REM EPLICAIIA Elaillletertycete et tersciee «cis: <icis cicttclee-s.c:clocls occ Cen 
Dorsal and ventral valves respectively. 
Profile view of the same specimen. Galena shales near Cannon Falls, Minn. 
Minnesota Geological Survey collection. 
354 
361 
381 
383 
